Any suggestions on spacing out three fins?

Make a template by rolling a strip of paper around the tube, and marking the point of overlap. Unroll it, and the marks are the circumference of the tube. Measure, divide by 3, put back on tube, mark each fin position.

Brett

Damn you Jerry!! How do I get epoxy off and LCD screen? 8-)

A firestarter grain ignited and pressed against it.

May I send anyone a copy of AIR-10?

rmr special May 2005 shipping offer:

Provide your address in email. You may pay when and how you wish this month.

Jerry

TWO DOLLARS SHIPPING! jerry it's just a piece of paper, you could mail it for the price of a stamp.

I assume you're trying to amke an Estes style fin marking template for your tube. And it's not one of the MR sizes covered by the really useful yellow Estes marking guide templates.

There's a nice trick you can do here. If you use LINED notebook paper, with the lines running horizontal, then after removing it from the tube lay a ruler at an angle on the paper so it crosses a multiple of 3 lines. Draw that line. The intersections with the lines that are the multiples of 3 mark your fin locations. You can use the lines as guides and fold creases at those locations for a perfect marking template.

Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!

Unfortunately, in my case the rocket is much too big for lined notebook paper unless someone has a notebook with 36" long pages.

I figured out what I am going to do. I calculated the circumference of the centering rings and divided by 3. I am going to take a piece of string the same length as the circumference and mark it where the fins should go. I will wrap this around the centering rings and mark the fin locations.

This will get my fins within 1/2 inch and that is good enough for the size rocket I am building.

Brian Elfert

Tape several sheets together.

Pi times D = Circumference.

Cut a strip of paper this long.

Divide by three for three fins. Draw lines at those measurements.

Wrap around tube like Estes style fin marking guide.

Hopefully you know what to do from that point on.

I used my handy laser level. Put tube horizontal on flat surface, set laser to draw horizontal line, and trace one line. Then use the paper strip method to create other two lines using the first line as an index.

Brian Elfert wrote:

notebook

Cool! A brilliant and innovative way to cheaply, and easily; perform the classic drafting technique of dividing a line segment into "x" equal segments.

He'd rather have his fins off by up to 1/2". He said so.

Stand the tube up on a large sheet of paper, and draw around the tube, marking its circumference on the paper. Remove the tube.

Draw a couple of straight lines that each intersect the circle in two places.

Draw new lines perpendicular to each of these original lines, centred on each line. Use a compass placed at the line / circle intersections to draw little intersecting arcs on either side of the lines, which you can then connect to form the perpendiculars centred on these lines without measuring anything.

These new perpendicular lines will intersect at the centre of the circle. Using a protractor, mark out and then extend three lines, 120 degrees apart, from the centre of the circle.

Put your motor tube back on the original circle, and transfer to it the locations of the three lines that are 120 degrees apart.

Using a piece of angle stock, extent these lines up the motor tube, as your fin guides.

This same technique can be used to locate and mark the fin slots for your airframe.

The paper you were drawing on makes a good visual fin guide when you glue the fins on. If drawn on thicker stock you can cut out the circle and the extended fin lines to make a template that can be slid onto the tube and over the fins to keep everything aligned while the adhesive sets.

...Rick

Give me a break. I would rather have them perfect, but 1/2" off won't be noticeable on a large rocket.

The most important thing is to have the fins straight up and down.

Brian Elfert

And it's such an old trick, I can't even remember for sure where I learned it from. Maybe my dad, maybe someone else, but I've been using it for a LONG time, longer than many rocketeers have been alive.

Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!

As I said.

Brian Elfert wrote in news: snipped-for-privacy@corp.supernews.com:

Now I'm just a simple cardboard and balsa jockey, but seems to me you can do this job with a piece of string and marker. No calculation, no ruler.

Take the string, wrap it around your centering ring, clip it or mark the length. There's your circumference of a value that you need not be concerned about.

Take the string and fold the length that represents the circumference into equal thirds. (letter z collapsed down on itself) Mark the two bends with the marker.

Wrap the string around the ring and mark the start, and where the two marks that were at the folds are on the ring. Do the same with the 2nd and subsequent rings.

Seems simple to me. Just increase the number of equal string folds for any number of fins you want.

ScottE - Engineers Know the Math, but Make the Jig

Use a compass... 120 degrees apart for 3 fins... not too hard... you don't need to have the whole thing laid out on 360 degrees... you only need baseline to 120 degrees... mark and spin the can just once... easy.

~ Duane Phillips.